What is sulfamethoxazole/trimethoprim?

Sulfamethoxazole/trimethoprim is an antibacterial prescription combination medicine approved by the U.S. Food and Drug Administration (FDA) to treat certain infections, such as:

Acute exacerbations (worsening) of chronic bronchitis;

Urinary tract and acute ear infections;

Shigellosis;

Diarrhea;

Pneumocystis carinii pneumonia (PCP).

Sulfamethoxazole/trimethoprim is also FDA-approved to prevent PCP in people who are immunosuppressed and are at risk of developing PCP.

Shigellosis and PCP are opportunistic infections. An opportunistic infection is an infection that occurs more frequently or is more severe in people with weakened immune systems -- such as those infected with HIV -- than in people with healthy immune systems.

Sulfamethoxazole/trimethoprim can also be used "off-label" to prevent and treat other opportunistic infections of HIV infection. "Off-label" use refers to use of an FDA-approved medicine in a manner different from that described on the medicine label. Good medical practice and the best interests of a patient sometimes require that a medicine be used "off-label."

What HIV-related opportunistic infections is sulfamethoxazole/trimethoprim used for?

The Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents, prepared by the U.S. Department of Health and Human Services (HHS) and the Centers for Disease Control and Prevention (CDC), includes recommendations on the HIV-related uses of sulfamethoxazole/trimethoprim to:

Prevent:

PCP from occurring the first time (called primary prophylaxis) and from recurring (called secondary prophylaxis or maintenance therapy).

What should I tell my health care provider before taking sulfamethoxazole/trimethoprim?

If you are allergic to sulfonamides (including sulfamethoxazole), trimethoprim, or any other medicines.

About any medical conditions you have or have had, for example, diabetes or liver problems.

About anything that could affect your ability to take medicines, such as difficulty swallowing or remembering to take pills.

If you are pregnant or plan to become pregnant. Whether sulfamethoxazole/trimethoprim can harm an unborn baby is unknown. Sulfamethoxazole/trimethoprim should not be used by pregnant women because sulfonamides (including sulfamethoxazole) may cause kernicterus.

If you are breastfeeding or plan to breastfeed. Do not breastfeed if you are infected with HIV.

About other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Ask your health care provider if there are interactions between sulfamethoxazole/trimethoprim and the other medicines you take.

Ask your health care provider about possible side effects from sulfamethoxazole/trimethoprim. Your health care provider will tell you what to do if you have side effects.

How should I take sulfamethoxazole/trimethoprim?

Take sulfamethoxazole/trimethoprim according to your health care provider’s instructions. Your health care provider will tell you how much sulfamethoxazole/trimethoprim to take and when to take it. Before you start sulfamethoxazole/trimethoprim and each time you get a refill, read any printed information that comes with your medicine.

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